Effects of Conversion Parameters on the Transport Properties of YBCO Films in the BaF 2 Ex Situ Process
- PDF / 2,830,257 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 47 Downloads / 219 Views
The effects of conversion parameters on transport properties of YBa2Cu3O7−␦ (YBCO) films on rolling assisted biaxially textured substrates (RABiTS) in the BaF2 ex situ process were investigated for total pressures Ptotal between 0.1 and 1.3 atm, water vapor pressures PH2O between approximately 7 and 70 Torr and processing temperatures TS between 700 and 790 °C. For this study, a 0.3-m-thick Y–BaF2–Cu–O precursor film was deposited on a 1-cm-wide Ni⳱3 at.% W RABiTS with a buffer layer architecture of CeO2/YSZ/Y2O3/Ni deposited in single passes in various reel-to-reel systems for each layer. Under the conditions of Ptotal ⳱ 0.1 atm, TS ⳱ 740 °C and PO2 approximately 150 mTorr, JC > 2 MA/cm2 was obtained at 77 K and self field for PH2O 艋 20 Torr. At higher PH2O (⳱70 Torr), however, the maximum attainable JC decreased. In addition, the JC at these higher PH2O dropped rapidly with increased dwell time. The highest JC, 2.5 MA/cm2, was achieved at 730 °C with Ptotal ⳱ 0.1 atm and PH2O approximately 7 Torr. Finally, the variation of IC with wet conversion time was performed at each processing temperature.
I. INTRODUCTION
YBa2Cu3O7−␦ (YBCO) based coated conductors have been developed for applications in high-temperature superconductivity (HTS) for power transmission cables and high-field magnets due to their potential for high critical current density JC at 77 K under high magnetic field. Several methods to produce long-length substrates for high-performance coated conductors have been explored, namely, ion-beam-assisted deposition (IBAD),1,2 rolling assisted biaxially textured substrates (RABiTS),3,4 and inclined substrate deposition (ISD).5,6 These methods can result in quasi-single-crystal templates where highquality epitaxial YBCO films are subsequently deposited. In the IBAD and ISD approaches, yttria-stabilized ZrO2 (YSZ) or MgO buffer layers are grown cubetextured on randomly oriented polycrystalline Ni-alloy substrates by high-energy ion-beam assistance or through the adjustment of the angle between the substrate and flux of evaporated materials. The YBCO layers are then a)
Address all correspondence to this author. e-mail: [email protected] b) Present address: University of Cambridge, Pembroke St. Cambridge, United Kingdom c) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/publications/jmr/policy.html. DOI: 10.1557/JMR.2004.0166 J. Mater. Res., Vol. 19, No. 4, Apr 2004
http://journals.cambridge.org
Downloaded: 24 Mar 2015
deposited by in situ or ex situ techniques. In the RABiTS approach, cube-textured Ni or Ni-alloy is produced by cold rolling followed by a recrystallization heat treatment. Buffer layers such as Y2O3, YSZ, and CeO2 are then subsequently grown epitaxially on the textured metals. Efforts to enhance texture quality of all these substrates continue in an attempt to achieve higher JC values for the YBCO layers. For all approaches (IBAD, RABiTS, and ISD)
Data Loading...
